Cardiovascular disease ranks as a leading cause of mortality and morbidity and represents a significant drain on health resources in many countries.
It is well established that aspirin therapy reduces the risk of a stroke and a first heart attack in healthy individuals, and subsequent heart attacks, strokes, or cardiovascular death in patients with established cardiovascular disease. For example, U.S. Pat. No. 5,240,917 relates to the percutaneous administration of aspirin as an antithrombotic agent.
Studies have shown that aspirin reduces the risk of cardiovascular events by as much as 25% in patients with arterial vascular disease. Most heart attacks and strokes are caused by blood clots in the heart or brain arteries that form on top of cracked atherosclerotic plaques. These blood clots are predominantly composed of clumped platelets. Aspirin works to prevent blood clot formation at these sites by reducing the ability of the platelets to clump together and form platelet aggregates. Aspirin, also known as acetylsalicylic acid, reduces platelet reactivity because its acetyl group acetylates a key intra-platelet enzyme known as cyclo-oxygenase. Once acetylated, cyclo-oxygenase cannot work to generate thromboxane A2, a substance released from the platelets that serves to activate other platelets and induce them to clump together in aggregates. In order for aspirin to work, therefore, it must reduce thromboxane A2 levels.
Thromboxane A2 has a very short half-life, and is rapidly converted to a stable metabolite called thromboxane B2. Although thromboxane B2 can be measured in blood, the tests can be problematic because platelets can be activated during the collection process. Once activated, the platelets will release thromboxanes that can interfere with the assay. It is therefore preferable to measure thromboxane B2 in the urine.
Even though platelets are an important part of blood clots, rapid technology to measure and predict platelet physiology is lacking. Some accepted laboratory methods include:                i) Bleeding Time, a test which is qualitative, not quantitative;        ii) Platelet Aggregometry. This test measures the clumping of platelets in response to various stimuli. The test is arduous, time-consuming, and expensive and is not specific for the effects of aspirin on platelet activation; and        iii) Tests of platelet activation using fluorescent cell sorting techniques. This test can only be done on freshly collected blood and uses size separation to separate platelets from other blood cells and fluorescently-tagged antibodies to identify activated platelets. This test is cumbersome and does not provide aspirin-specific information.        
The present invention provides a novel method for assessing platelet function and correlating a readout of that function with the risk of a cardiovascular event.
Aspirin is effective for patients with heart attacks, strokes or peripheral arterial disease or those at risk of these disorders. Aspirin has also been shown to be effective in reducing the incidence of pregnancy-induced hypertension and pre-eclamptic toxicity in women at risk. A role for aspirin in reducing the risk of fatal colon cancer has also been suggested and aspirin may be useful in the treatment of patients with antiphospholipid antibodies, including the lupus anticoagulant. Thus, determining the effectiveness of aspirin treatment in many conditions is an important prognostic factor and may help physicians recommend the most appropriate therapeutic course.
While aspirin is effective in many individuals, approximately 10 to 20% of patients with arterial thrombosis who are treated with aspirin have a recurrent vascular event during long-term follow-up. The failure of these patients to derive a beneficial effect from aspirin is termed “aspirin resistance”. There are several possible explanations for aspirin resistance but, whatever the underlying cause, the result is the same. It would obviously be beneficial to be able to identify those patients who are aspirin resistant in order to help physicians determine the advisability of altering the aspirin dose or administering alternative or additional anti-platelet therapies. A need therefore exists for a simple method to accurately determine the response to aspirin and predict the likelihood of onset of a cardiovascular event or other medical condition that would benefit from lowering of thromboxane-A2 levels.